Patent Pending: Yamaha XS400 “Roadster”

Innovative XS400 from Roman Juriš…  

Introduced in 1976, the Yamaha XS400 came during a time when the major manufacturers were foreseeing the end of the two-stroke era and turning their attention to the development of four-stroke street bikes. The middleweight XS was intended more as a reliable workhorse commuter than a sporting machine, competing against machines such as the Kawasaki KZ400, Suzuki GS400, and Honda 400 Hawk.

The air-cooled parallel-twin offered 45 horsepower and the bike turned the quarter-mile in 14.58 seconds, faster than most of the competition and only 0.4 seconds slower than Yamaha’s own two-stroke RD400F. Not bad, but the little 400 four-stroker wouldn’t spur any road racers or canyon riders to wax poetic.

“Neither the fastest in its class, nor the least expensive, nor the most comfortable. It is nevertheless a handsome, functional and economical motorcycle — easy to maintain, miserly with gas, and still competitive in a hotly contested class.” –Cycle, via Motorcycle Classics

Our friend Roman Juriš of Slovakia, builder of the recent KTM 990 Super Duke we featured, picked up this ’84 XS400 as a non-running donor for an extensive build.

“I wanted a simple roadster, clean lines, slim build, something like the good old 1976 Laverda 750 or 1967 Honda CB250, but in a modern design.”

Most importantly, Roman wanted to test a new front suspension concept he’s been developing, a Progressive Upside Down Fork (PUSDF) assembly intended to minimize dive under braking — a system he’s in the process of patenting. There are three patent claims:

1. Progressiveness — for example, for a 120 mm suspension travel of the wheel, there is a 60 mm lift in the fork.

2. When springing, the axis of the front wheels is pushed forward and thus eliminates the shortening of the wheelbase.

3. Separation of spring and braking force — the motorcycle does not dive when braking.

Only the engine and some of the wiring remain from the original donor — Roman built the entire frame from scratch, and the XS is now running a shortened YZF125 swingarm, supermoto wheels, custom bodywork with a lovely speed block livery, and that unique front suspension assembly:

“The front fork is purposefully brand new and protected by a world patent.”

Roman is waiting for the cold Slovakian weather to clear so he can test the new front suspension system. We can’t wait to hear how it goes!

Yamaha XS400 Cafe Racer: Builder Interview

• Please tell us a bit about yourself, your history with motorcycles, and your workshop.

I’m a hobby motorcycle modifier and I do it for my own pleasure.

• What’s the make, model, and year of the donor bike?

Yamaha XS400, year 1984.

• Why was this bike built?

At the end of 2018, I thought there’d been no new news in motorcycle front suspension for a long time. I had a possible solution, but I knew that I didn’t want to install the new front fork on a regular motorcycle.

My idea was a roadster with an undermounted engine and a backbone frame. In January 2019, I bought a non-riding Yamaha XS400 and started making a completely new frame and actually everything related to building a motorcycle.

• What was the design concept and what influenced the build?

I wanted a simple roadster, clean lines, slim build, something like the good old 1976 Laverda 750 or 1967 Honda CB250, but in a modern design.

• What custom work was done to the bike?

I only used the engine and part of the wiring from the original motorcycle. The frame is completely new.

The wheels were originally motard, but they have modified hubs and strings. The rear swingarm comes from a Yamaha YZF 125 but is shortened and equipped with a spring unit placed in the style of a Ducati Scrambler.

The front fork is purposefully brand new and protected by a world patent.

The whole design was modeled from clay and the parts are made of fiberglass. The paintwork is in the style of Yamaha racing motorcycles from the seventies of the last century.

 

The muffler is under the seat, the on-board instrument is my favorite Koso. The motorcycle is not street legal, but it has all the elements of a homologated vehicle. I wanted to prove that even a bike with rearview mirrors, turn signals, and mudguards can look good.

• Does the bike have a nickname?

It has the name Roadster – it is a tribute to the Jawa 90 Roadster that was produced in Slovakia some time ago. It was a great bike that was ahead of its time.

• Any idea of horsepower, weight, and/or performance numbers?

The engine is fully stock. (I need to find out the weight.)

• Can you tell us what it’s like to ride this bike?

The motorcycle is so fresh and the weather in Slovakia so cold that the bike has not yet been tested.

• Was there anything done during this build that you are particularly proud of?

Front fork.

• Is there anyone you’d like to thank?

To my wife, for allowing me to work about 3,000 hours on this project over five years. To all friends who did a great job welding, painting and upholstery. And to those who didn’t close the door when they saw me coming.

Build Process Photos

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